Constant-velocity fixed joints may comprise an outer joint part with outer ball tracks, an inner joint part with inner ball tracks, torque transmitting balls which are guided in pairs of tracks each formed of an outer and an inner ball track, and a ball cage with circumferentially distributed cage windows in which the balls are received. Here, the balls are held in a common central plane and are guided onto the bisecting plane when the joint is deflected. Constant-velocity rotary joints of this type are known as Rzeppa fixed joints (RF) or as undercut-free fixed joints (UF).
U.S. Pat. No. 6,319,133 has disclosed a constant-velocity rotary joint having undercut-free ball tracks, the ball tracks of the outer joint part having in each case convexly curved inner sections and, toward the opening side, end sections which are in each case curved concavely in an opposite direction with respect to the former.
U.S. Pat. No. 5,782,696 has disclosed a constant-velocity rotary joint having undercut-free ball tracks, the curvature center points of the ball tracks being offset axially with respect to the central plane.
Development in automotive engineering demands increased performance of the known constant-velocity rotary joints. This means that, with the predefined installation space and predefined mass, the service life and functional scope are to be increased or that, with the predefined service life and functional scope, the installation space and the mass are to be reduced. Here, the difficulty lies in the interrelationship between the size of the joint on one side and its strength and service life on the other.
U.S. Pat. No. 5,509,857 has disclosed a constant-velocity rotary joint as a Rzeppa fixed joint with continuously curved ball tracks with undercuts. The balls have a diameter BD and lie on the pitch circle diameter BCD about the joint center point M. It is said that the ratio between the pitch circle diameter PCD and the ball diameter BD usually lies between 3.1 and 3.5. With regard to a high stability of the constant-velocity rotary joint, it is cited as particularly advantageous to select the ratio between the pitch circle diameter PCD and the ball diameter BD to be greater than 3.5.